filtration and backwashing n.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
FILTRATION AND BACKWASHING PowerPoint Presentation
Download Presentation
FILTRATION AND BACKWASHING

Loading in 2 Seconds...

play fullscreen
1 / 39

FILTRATION AND BACKWASHING - PowerPoint PPT Presentation


  • 338 Views
  • Uploaded on

FILTRATION AND BACKWASHING. A. Amirtharajah School of Civil and Environmental Engineering Georgia Institute of Technology Atlanta, GA 30332. FILTRATION: THE GREAT BARRIER TO PARTICLES, PARASITES, AND ORGANICS. Particle Removal. Improve taste, appearance Sorbed metals and pesticides

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'FILTRATION AND BACKWASHING' - fiachra-philbin


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
filtration and backwashing

FILTRATION AND BACKWASHING

A. Amirtharajah

School of Civil and Environmental Engineering

Georgia Institute of Technology

Atlanta, GA 30332

particle removal
Particle Removal
  • Improve taste, appearance
  • Sorbed metals and pesticides
  • Pathogens: bacteria, viruses, protozoa
organic removal in biofiltration
Organic Removal in Biofiltration
  • Prevent biofouling of distribution system
  • Remove DBP precursors
multiple barrier concept
Multiple-Barrier Concept

chemical addition

direct filtration

filtration

watershed protection

sedimentation

disinfection

raw water

distribution system

screen

coagulation

flocculation

waste sludge

backwashrecycle

waste sludge

fundamental and microscopic view
Fundamental and Microscopic View

1. Filtration:

  • Attachment
  • Detachment

2. Backwashing:

  • Detachment
mechanisms of filtration
Mechanisms of Filtration

particle, dp

transport

fluid streamline

attachment

collector, dc

detachment

history of filtration theory 1
History of Filtration Theory(1)

Phenomenological - Macroscopic View

Basic Equations:

Ives:

trajectory theory
Trajectory Theory

dp

Viruses

0.01 -0.025 mm

Bacteria

0.2 -1mm

Cryptosporidium

3 - 5mm

Giardia

6 - 10mm

dc

dc

dc

Diffusion

dp < 1 mm

Sedimentation

dp > 1 mm

Interception

history of filtration theory 2
History of Filtration Theory (2)

Trajectory Analysis - Microscopic View

filter effluent quality
Filter Effluent Quality

Filter Ripening

Outlet

Backwash remnants

TB

above

media

in

media

TM

Effluent Turbidity

Function

of influent

Clean back-wash

Media

Strainer

TU

Filter breakthrough

TU

TM

TB

TR

Time

conceptual model of filtration
Conceptual Model of Filtration

Attachment(+) 

Filter coefficient ()

0

(-) Detachment

Filter

Ripening

Effective

Filtration

Turbidity

Breakthrough

Wormhole

Flow

Time

slide18
Question:

Why is it easier to remove alum or clay particles in contrast to polymer coated particles or micro-organisms during backwash?

sphere flat plate interactions 1
Sphere - Flat Plate Interactions (1)

Van der Waals Force:

a

z

Electrostatic Double Layer Force:

detachment during backwashing
Detachment During Backwashing

Hydrodynamic Forces > Adhesive Forces

1. Spherical Particles - pH and Ionic Strength

2. Non-spherical Particles - Ionic Strength

  • Kaolinite Platelets
backwashing filters
Backwashing Filters
  • Weakness of fluidization backwash
  • Improvement due to surface wash
  • Collapse-pulsing air scour

The best for cleaning

theory for collapse pulsing
Theory for Collapse-Pulsing

a, b = coefficients for a given media

Qa = air flow rate

Percentage of minimum fluidization

water flow

biofiltration
Biofiltration
  • Ozonation
  • Microbial counts in effluent
  • Head loss
  • Effect of biocides
  • Particle removal
biological filtration and backwashing
Biological Filtration and Backwashing
  • Precursor Removal
  • Minimize DBP’s
  • Effect of Hydrophobicity
bacterial adhesion
Bacterial Adhesion

Energy barrier

Repulsion

Potential Energy of Interaction

Distance

Secondary

Attraction

minimum

Release of

extracellular

polymeric substances at

secondary minimum

Primary minimum

backwashing biofilters
Backwashing Biofilters
  • Collapse-pulsing air scour
    • Cleans better
    • No deleterious effect
  • Chlorinated backwash reduces TOC removal over time
  • Chloraminated backwash less than 2.0 mg/L may be used
pathogenic protozoa
Pathogenic Protozoa
  • Low infective doses
  • Resistant to chlorine disinfection
  • Analytical techniques
outbreaks of cryptosporidiosis
Outbreaks of Cryptosporidiosis
  • Surface and groundwater sources
  • Runoff
  • Sewage spills
  • Coagulation
  • Filtration
    • rate changes
  • Backwash recycle
  • Contaminated distribution system
particle counts
Particle Counts
  • Continuous on-line monitoring
  • Low operating costs
  • High sensitivity
  • Detachment of aggregates
cyst removal vs particle removal
Cyst Removal vs Particle Removal

Nieminski and Ongerth (1995)

minimizing risk of outbreaks
Minimizing Risk of Outbreaks
  • Optimal destabilization of particles
  • Filter-to-waste
  • Coagulants in backwash
  • Slow-start filtration
  • Minimizing flow rate changes in dirty filters
  • Treatment of backwash water
  • Filter effluent turbidity < 0.1 NTU
concluding statement
Concluding Statement

In the multiple-barrier concept, filtration is the “great” barrier to particles, parasites and organics.

summary and conclusions
Summary and Conclusions
  • Importance of particle destabilization
  • Micromechanical force model
  • Biofiltration for organics removal
  • Effectiveness of collapse-pulsing air scour
  • Multiple-barrier concept
references
References
  • Amirtharajah, A., “Some Theoretical and Conceptual Views of Filtration,” JAWWA, Vol. 80, No. 12, 36-46, Dec. 1988.
  • Amirtharajah, A., “Optimum Backwashing of Filters with Air Scour - A Review,” Water Sci. and Tech., Vol. 27, No. 10, 195-211, 1993.
  • Ahmad, R. et al., “Effects of Backwashing on Biological Filters,” JAWWA, Vol. 90, No. 12, 62-73, Dec. 1998.
acknowledgments
Acknowledgments

This paper includes the work of several former students at Georgia Tech:

M.S. students T.M. Ginn, L. Zeng and X. Wang and Ph.D students, Drs. P. Raveendran, R. Ahmad, K.E. Dennett and T. Mahmood.

They were not only students but teachers too! Their work is acknowledged with gratitude.